In Chapter One of Alas, Babylon, Pat Frank uses a Biblical phrase imbued with symbolic meaning to foreshadow the realized threat of nuclear war.
Randy Bragg and his brother Mark, who now works for the SAC, created a secret code to warn of coming danger. "Alas, Babylon" is a Biblical reference, taken from Revelation 18:10, and refers God's judgment upon a powerful city. Mark and Randy both remember the pastor from their childhood, who thundered about God's wrath from the pulpit, "Alas, Babylon!"
Now they use the quote, "Alas, Babylon" to symbolize imminent disaster--possibly in the form of nuclear war. When Randy receives the "Alas, Babylon" message at the end of one of Mark's telegram, he fears the worst, but prepares for the possible coming disaster.
Pat Frank alludes to God's judgment in the final days through the Biblical quote "Alas, Babylon" through the Bragg brothers' secret code on the telegram.